Black holes regulate cool gas accretion in massive galaxies.

The nucleus of almost all massive galaxies contains a supermassive black hole (BH) 1 . The feedback from the accretion of these BHs is often considered to have crucial roles in establishing the quiescence of massive galaxies 2-14 , although some recent studies show that even galaxies hosting the most active BHs do not exhibit a reduction in their molecular gas reservoirs or star formation rates 15-17 . Therefore, the influence of BHs on galaxy star formation remains highly debated and lacks direct evidence. Here, based on a large sample of nearby galaxies with measurements of masses of both BHs and atomic hydrogen (HI), the main component of the interstellar medium 18 , we show that the HI gas mass to stellar masses ratio (μ HI  = M HI /M ⋆ ) is more strongly correlated with BH masses (M BH ) than with any other galaxy parameters, including stellar mass, stellar mass surface density and bulge masses. Moreover, once the μ HI -M BH correlation is considered, μ HI loses dependence on other galactic parameters, demonstrating that M BH serves as the primary driver of μ HI . These findings provide important evidence for how the accumulated energy from BH accretion regulates the cool gas content in galaxies, by ejecting interstellar medium gas and/or suppressing gas cooling from the circumgalactic medium.